A significant body of prior art relating to IVT machines of the above type exists. Typical examples of these are described in the following publications: relating to bicycles—U.S. Pat. No. 4,878,883, GB2062142A, GB2135743A, U.S. Pat. Nos. 4,618,331, 3,956,944, 4,832,660, 5,984,814 and U.S. Pat. No. 4,787,879; relating to CVT/IVT—WO03/042575 and WO03/078869; relating to grooved/ribbed cone disc engagement—WO01/75333 and U.S. Pat. No. 4,367,067; relating to variable sprocket teeth ladder chain—WO94/04411 and U.S. Pat. No. 5,406,863.
It will be seen from the specifications of U.S. Pat. No. 4,878,883, GB2062142A, GB2135743A, U.S. Pat. Nos. 4,618,331, 3,956,944, 4,832,660, 5,984,814 and U.S. Pat. No. 4,787,879 that these machine consist largely of radially positionable engagement devices that operate, either by means of sprocket teeth or frictionally, within fixed tracks, which are spaced radially about a variable sprocket hub. Because of the limited number of engagement devices the flexible member track around them does not constitute a circular arc and their outputs are as a result, pulsed. Another problem with these prior art machines is the non-exact synchronisation of their engagement devices with drive chain links where engagement is accomplished via spring-loaded sprocket teeth or rotatable full sprockets operating in the fixed guides which make these devices suitable only for low speed applications, for example on bicycles. In high speed and high torque applications the above prior art machines are unsuitable.
In the cases of WO03/042575 and WO03/078869 the synchronisation problems have largely been solved, but they rely on sprag clutches which do not provide for power transmission in both directions (do not allow for engine braking).
In the cases of WO01/75333 and U.S. Pat. No. 4,367,067 the positive synchronised engagement of the chain with the disc grooves/ribs again presents a synchronisation problem.
In the cases of WO94/04411 and U.S. Pat. No. 5,406,863 positive engagement is accomplished but the storage of the ladder chain as well as its adjustment presents a problem in high speed applications.
The devices in most of the above publications sacrifice synchronised positive engagement for the ability to vary the ratio in infinitely small increments.